/* kitty: C++ truth table library
 * Copyright (C) 2017-2019  EPFL
 *
 * Permission is hereby granted, free of charge, to any person
 * obtaining a copy of this software and associated documentation
 * files (the "Software"), to deal in the Software without
 * restriction, including without limitation the rights to use,
 * copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following
 * conditions:
 *
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
 * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
 * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
 * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 * OTHER DEALINGS IN THE SOFTWARE.
 */

/*!
  \file hash.hpp
  \brief Implements hash functions for truth tables

  \author Mathias Soeken
*/

#pragma once

#include <cstdint>
#include <cstdlib>

#include "static_truth_table.hpp"

namespace kitty {

/*! \brief Hash function for 64-bit word */
inline std::size_t hash_block(uint64_t word) {
    /* from boost::hash_detail::hash_value_unsigned */
    return word ^ (word + (word << 6) + (word >> 2));
}

/*! \brief Combines two hash values */
inline void hash_combine(std::size_t& seed, std::size_t other) {
    /* from boost::hash_detail::hash_combine_impl */
    const uint64_t m = UINT64_C(0xc6a4a7935bd1e995);
    const int r = 47;

    other *= m;
    other ^= other >> r;
    other *= m;

    seed ^= other;
    seed *= m;

    seed += 0xe6546b64;
}

/*! \brief Computes hash values for truth tables */
template <typename TT>
struct hash {
    std::size_t operator()(const TT& tt) const {
        auto it = std::begin(tt._bits);
        auto seed = hash_block(*it++);

        while (it != std::end(tt._bits)) {
            hash_combine(seed, hash_block(*it++));
        }

        return seed;
    }
};

/*! \cond PRIVATE */
template <int NumVars>
struct hash<static_truth_table<NumVars, true>> {
    inline std::size_t
    operator()(const static_truth_table<NumVars, true>& tt) const {
        return hash_block(tt._bits);
    }
};
/*! \endcond */
} // namespace kitty
